Cardiac pacing by an artificial pacemaker provides an electrical stimulation of the heart when its own natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at rates and intervals sufficient for a patient's health. Such antibradycardial pacing provides relief from symptoms and even life support for hundreds of thousands of patients. Cardiac pacing may also provide electrical overdrive stimulation to suppress or convert tachyarrhythmias, again supplying relief from symptoms and preventing or terminating arrhythmias that could lead to sudden cardiac death.
Cardiac pacing by currently available or conventional pacemakers is usually performed by a pulse generator implanted subcutaneously or sub-muscularly in or near a patient's pectoral region. Pulse generator parameters are usually interrogated and modified by a programming device outside the body, via a loosely-coupled transformer with one inductance within the body and another outside, or via electromagnetic radiation with one antenna within the body and another outside. The generator usually connects to the proximal end of one or more implanted leads, the distal end of which contains one or more electrodes for positioning adjacent to the inside or outside wall of a cardiac chamber. The leads have an insulated electrical conductor or conductors for connecting the pulse generator to electrodes in the heart. Such electrode leads typically have lengths of 50 to 70 centimeters.
Although more than one hundred thousand conventional cardiac pacing systems are implanted annually, various well-known difficulties exist. For example, a pulse generator, when located subcutaneously, presents a bulge in the skin that patients can find unsightly, unpleasant, or irritating, and which patients can subconsciously or obsessively manipulate. Even without persistent manipulation, subcutaneous pulse generators can exhibit erosion, extrusion, infection, and disconnection, insulation damage, or conductor breakage at the wire leads. Although sub-muscular or abdominal placement can address some concerns, such placement involves a more difficult surgical procedure for implantation and adjustment, which can prolong patient recovery.
A conventional pulse generator, whether pectoral or abdominal, has an interface for connection to and disconnection from the electrode leads that carry signals to and from the heart. Usually at least one male connector molding has at least one terminal pin at the proximal end of the electrode lead. The male connector mates with a corresponding female connector molding and terminal block within the connector molding at the pulse generator. Usually a setscrew is threaded in at least one terminal block per electrode lead to secure the connection electrically and mechanically. One or more O-rings usually are also supplied to help maintain electrical isolation between the connector moldings. A setscrew cap or slotted cover is typically included to provide electrical insulation of the setscrew. This briefly described complex connection between connectors and leads provides multiple opportunities for malfunction.
Other problematic aspects of conventional pacemakers relate to the separately implanted pulse generator and the pacing leads. By way of another example, the pacing leads, in particular, can become a site of infection and morbidity. Many of the issues associated with conventional pacemakers are resolved by the development of a self-contained and self-sustainable pacemaker, or so-called leadless pacemaker.
Similar to active fixation implantable leads used with conventional pulse generators, leadless pacemakers are typically fixed to an intracardial implant site by an actively engaging mechanism such as a screw or helical member that threads into the myocardium. Leadless pacemakers are often delivered to an intracardial implant site via a delivery system including a delivery catheter. Conventional delivery catheter systems are typically long (e.g., approximately 42 mm or longer), making navigation of the patient anatomy difficult and increasing a footprint of the system at the implant site.
Some conventional delivery systems are tether based in which attachment of the leadless pacemaker to the delivery catheter is dependent on the tether alignment. Once the tether alignment is lost, which may occur due to system tolerances or anatomical interferences, among other factors, the leadless pacemaker may spontaneously release from the delivery catheter. Such a spontaneous release may cause embolism, a need to retrieve the leadless pacemaker, and/or other patient risks. Retrieval may be performed by removing the delivery catheter and introducing a retrieval catheter to remove the leadless pacemaker. The delivery catheter system is generally different in structure and operation from the retrieval catheter system, which increases procedure time, complexity, and cost. If retrieval cannot be performed using a retrieval catheter system, the leadless pacemaker is typically retrieved through surgery, further complicating the procedure. Moreover, implanting a second leadless pacemaker into a patient often requires the use of a second catheter delivery system, as many conventional catheter systems fail to accommodate bed-side loading of leadless pacemakers onto a previously used catheter system. Instead, many conventional catheter systems are preloaded during manufacturing. It is with these observations in mind, among others, that the presently disclosed technology was conceived and developed.